Thermal cycling switch

ABSTRACT

A thermal cycling switch in which the main bimetal and the ambient compensating bimetal are supported from a common terminal with the adjustable means for the differential setting extending between the compensating bimetal and the main bimetal assembly. Also, the terminals for the switch are held by the switch casing in a way which braces the terminals against movement out of their normal position.

United States Patent [72] Inventor George C. Aldous Mansfield, Ohio 211 Appl. No. 21,013

[22] Filed Mar. 19, 1970 [45] Patented Jan. 11,1972

[ 73] Assignee Westinghouse Electric Corporation Pittsburgh, Pa.

I 54 I THERMAL CYCLING SWITCH 4 Claims, 4 Drawing Figs.

[52] U.S. Cl 337/101, 337/93, 337/375 [5 l] Int. Cl ..H0lh 37/14, HOlh 37/24, HOlh 61/08 [50] Field of Search 337/82, 95,

[56] References Cited UNITED STATES PATENTS 3,360,197 12/1967 Stringham 337/100 X 3,064,103 11/1962 Biermann et al. 337/82X 2,987,652 6/1961 Turnupseed..... 337/96 X 2,813,173 11/1957 Risacheretal. 337/99X Primary ExaminerBernard A. Gilheany Assistant Examiner- Dewitt M. Morgan Attorneys-F. H. Henson and E. C. Arenz ABSTRACT: A thermal cycling switch in which the main bimetal and the ambient compensating bimetal are supported from a common terminal with the adjustable means for the differential setting extending between the compensating bimetal and the main bimetal assembly. Also, the terminals for the switch are held by the switch casing in a way which braces the terminals against movement out oftheir normal position.

THERMAL CYCLING SWITCH BACKGROUND OF THE INVENTION 1. Field of the Invention The invention pertains to thermal cycling switches of the type typically used for controlling the rate of energization of electric heaters such as are used in range surface units.

2. Description of the Prior Art None of the prior art of which applicant is aware is particularly pertinent to the invention. However, patents considered illustrative of prior art constructions which my invention is intended to improve upon are as follows: US. Pat. Nos. 2,475,448; 2,623,137; 2,813,173; 2,906,839 and 3,110,789.

SUMMARY OF THE INVENTION In accordance with the invention, an improved thermal cycling switch is provided in which one of the principal features is the provision of a complete subassembly of the main bimetal heater assembly, an ambient compensator bimetal, and adjustable differential means, all supported from a common terminal. Another feature is the provision of terminals of a common shape and size secured to the casing for the switch in a manner which braces the terminals against undue movement.

DRAWING DESCRIPTION FIG. 1 is a front elevation of a thermal cycling switch according to the invention with the front cover portions of an indexing spring removed;

FIG. 2 is a sectional view corresponding to one taken along the line II-II ofFIG. 1;

FIG. 3 is an isometric view of a terminal according to the invention; and

FIG. 4 is a view of the back face of the switch and a wiring diagram showing the connections between a load and an electrical source.

DESCRIPTION OF THE PREFERRED EMBODIMENT The thermal cycling switch according to the invention includes an open-front, box shaped casing of square shape formed of rigid insulating material and including a base wall 11 and four sidewalls 12-15. The main cycling switch portion of the switch assembly as a whole includes a cycling contact 16 facing the adjusted contact 17. The cycling contact is carried at the free end of a deflectable main bimetal assembly generally designated 18. The adjusted contact is carried on a cam adjusted spring arm 19.

The main bimetal assembly 18 is of sandwich character and includes a bimetal strip 20, a resistance heater strip 21 spaced apart from the one face of the bimetal by a thin strip of mica 22, and having on the opposite face of the heater another strip of mica 23. The strips of mica serve to thermally and electrically insulate the bimetal from the heater. The clamps 24 are installed to hold the bimetal and heater in their described rela tionship.

The end of the bimetal opposite from the contact 16 is held in a metallic clamp 25 which has its inside surface insulated electrically from the bimetal. The end of the heater 21 which extends to the main clamp 25 is welded to the clamp along with the end of a leaf spring 26 which has its opposite end welded to terminal 27. The ends of the bimetal and of the heater are also welded to the cycling contact 16. The leaf spring serves as a pivot or hinge for the main bimetal assembly 18 which has a relaxed position, in the absence of the adjusting screw 28, in which the contact 16 end of the assembly is substantially closer to the wall 12 of the casing than is shown in FIG. 1. It will be appreciated then that the'main bimetal assembly includes the main bimetal and heater therefor, with the assembly also including means for pivotally securing that end of the assembly opposite the cycling contact to the terminal 27.

The ambient compensating bimetal is of right angle configuration as shown in FIG. I and includes one leg 29 which is welded along with the leaf spring 26 to the ter rninal 27, and another leg 30 which extends in the same general direction as the main bimetal assembly but only about as far as the leaf spring. The adjusting screw 28 is carried by the leg 30 of the ambient compensating bimetal by being turiied into an interiorly threaded bore 31 (FIG. 2) provided in the leg 30 opposite the main clamp 25. FIG. 2 also shows that the leg. 30 of the compensating bimetal is in face-to-face, but spaced apart, relationship with the bimetal assembly 18. Accordingly, the adjusting screw 28, besides serving as a mechanical link between the ambient compensator leg 30 and the main bimetal assembly, also provides a means for adjusting the main bimetal assembly initially for proper calibration.

The orientation of the main bimetal 20 is such that upon being heated the cycling contact 16 end of the bimetal 20 will move to the left in FIG. 1, and upon cooling the end moves back to the right.

To obtain an increased cycle length between the opening and closing of the contacts 16 and 17, the concept disclosed in US. Pat. No. 2,623,137is utilized in the main bimetal assembly. In essence, the heater 2] is of a character which expands in length during the initial stages of current flow to tend to deflect the contact 16 in a direction opposite to its normal direction of movement due to heat. Thus, additional time is required for the main bimetal 20 to overcome the negative deflection due to the heater 21 expansion, this phenomenon tending to hold the contacts closed for a longer time. The thermal insulation afforded by the mica strip 22 aids in the delay of the main bimetal reacting to the heater. After the contacts have opened and current flow through the heater 21 accordingly is terminated, the heater contracts in length to resist and delay the movement of the main bimetal 20 in its direction to the right resulting from normal cooling.

The ambient compensating bimetal performs the usual function of neutralizing main bimetal movement due to ambient temperature changes to which the main bimetal is subjected. Thus, the ambient compensator bimetal is oriented relative to the main bimetal to move in an opposite direction upon a change in ambient heat.

The thermal cycling switch is operated by the user by rotating a shaft 35 (FIGS. 1 and 2) journaled in the base wall 11. The shaft carries cam means providing three separate cam faces 36, 37 and 38. The upper cam face 36 works against an indexing spring 39 (only partially shown in FIG. 1) provided with an angular portion 39a which seats in either the indentation 36a as shown in FIG. 1 (corresponding to the off position of the switch), or the other indentatioii 36b (corresponding to the high heat position of the switch). It will be appreciated that additional indentations may spring cam face to indicate other degrees of heat.

The cam face 37 controls the cam adjusted spring 19 which carries the adjusted contact 17. In the position shown in FIG. 1, the switch is off and the angular portion 19a of the spring 19 seats in a shallow depression 37a of cam fac'e37. When the shaft is turned so that the spring bears against the large radius portion 37b of the cam, the switch is set for maximum heatwith the adjusted contact 17 shifted to its further'inost left position. Successive portions of the cam face 37 around the periphery thereof are of successively lesser radii so that the adjusted contact 17 is shifted successively further to the right to provide correspondingly shorter periods of switch on" time. In other words, with the cam 37 positioned to bias the adjusted contact 17 farther in the direction toward the cycling contact 16, the percentage of on time relative to the total cycling time will be increased since it takes longer for the main bimetal 20 to be heated and deflected away from the contact 17 of the cam adjusted spring 19. The cam face 38 cooperates with a current-carrying spring member 40 which has one end 41 secured to terminal 42, an angular portion 43 bearing against an indent 44 in the cam face 38 when the cam is in the position shown in FIG. 1. When the angular portion 43 of the be provided in the indexing spring is moved out of the indent 44, the free end of the spring 40 is deflected to the right (FIG. 1), so that the protruding tab portion 45 of the spring member 40 makes'contact with pilot light terminal 46, and end contact 47 of spring member 40 makes contact with a lineterminal 48. In an alternative arrangement, the spring 40 may also serve the purpose of the indexing spring 39 by providing a high heat indent at the ap propriate location on the cam face 38.

The connections between the electrical source, terminals and the load is shown in the wiring diagram of FIG. 4 in which the terminal locations on the back face of the base wall of the switch are also shown. The load 49 which is typically a range surface unit heater, is connected between the terminals 42 and 50, the terminal 40 being the one to which the end of the cam adjusted spring 19 is attached. The pilot light 51 has one side connected to neutral and its other side connected to the terminal 46 so that so long as the contacts 45 and 47 of currentcarrying spring member 40 are closed to their respective terminals, the voltage between one side of the line and neutral (e.g., 118 volts), will be provided across the pilot light. The main contacts 16 and 17 of the cycling switch are of course between the terminals 27 and 50 so that whenever the main contacts are closed, 236 volts is provided across the range surface unit 49.

For the purposes of standardization and cost economies, each terminal 27, 42, 46, 48 and 50 is ofa common shape and size. The general configuration of each terminal is best seen in FIG. 3 which is designated terminal 42 to correspond with the terminals shown in section in FIG. 2. Each terminal is adapted to be secured to the casing by staking. The lower portion 55 projects out of the back face of the base wall 11 of the casing and receives a flag-type connector or the like. The intermediate portion 56 is received in a slot 57 in the base wall provided for each terminal. The portions of the base wall 11 having the slots may be thicker than other portions of the base wall to accommodate the staking of the terminals. The opposite edges of the intermediate portion 56 are provided with shoulders 58 which seat on the inner face of the base wall 11 when the staking tabs 59 at the edges between the intermediate and projecting portions are set.

The portion of each terminal which projects upwardly into the interior of the casing includes a first leg 60 which is generally coplanar with the intermediate and lower portions of the terminal, and a second leg 61 bent out of the plane to form an approximately right angle corner with the first leg. The bottom edge 62 of the leg 61 is adapted to seat firmly on the base wall when the terminal is staked in place.

To further stabilize the terminal, abutments formed as a part of the casing proper are provided. The outer face of each leg 60, i.e., the face which is opposite to the direction in which the leg 61 extends, is located to be supported by an abutment. The abutment for terminal 42 is designated 63 in FIGS. 1 and 2. The abutment for pilot terminal 46 is 64, that for line terminal 27 is 66, that for terminal 50 is 65, and the abutment for line terminal 48 is not designated since it is a portion of the sidewall 13 of the casing. It will be appreciated that it need not be the outer face of the coplanar leg itself which directly bears against the abutment, since in connection with terminal 50 (FIG. 1) it will be seen that the end of the spring member 19 is interposed between that face and the abutment 65. Further, the abutments need not be the full height of the legs 60, but only of sufficient height, such as one-fourth to one-half the height of the leg, to adequately back up the leg.

It will be appreciated that with the shoulder and staking arrangement of the terminals, the terminals are held securely against edgewise movement. The arrangement of the lower edge of the right angle leg 61 seating on the base wall, and the abutment on the opposite side of the other leg braces the terminals against movement out of the plane of the terminal as a whole.

The general mode of operation of the switch described will be readily understood by those skilled in this art. The switch is shown in the off position in FIG. 1. By rotating the shaft in either direction so that the angular portion of the cam adjusted spring is moved off the shallow depression 370 the contact 17 is shifted to the left to bear against contact 16. Simultaneously, the spring arm 40 is moved to the right so that its contacts 45 and 47 touch the respective terminals 46 and 48 so that the circuits through the range surface unit 49 and the pilot light 51 are completed. If the switch is set by the user for high heat so that the spring 19 is riding on the portion 37b of the cam, the main bimetal assembly will be deflected substantially to the left and current will flow through the surface unit for a substantial time before the heater 21 develops sufficient heat to cause the bimetal 20 to deflect sufficiently further to the left to open the contacts 16 and 17. When the contacts 16 and 17 open, current flow through the surface unit 49 is terminated until'the bimetal 20 cools sufficiently that the contact 16 is brought back against contact 17 after the delay imposed by the initial contraction of the heater 21. During this period the pilot light remains energized even though there is no current flow through the surface unit since the l l8-volt circuit is completed between the terminals 46 and 48. If a portion of the cam surface 37 other than the high heat and the off position is utilized, the period of on time during which current flows through the surface unit will be proportionately less than at a high-heat position, and in accordance with radius of the cam surface 37 that the angular portion 19a bears against.

With the arrangement of parts as described, the switch casing may be of square form of about 1% inches on each side with the shaft axis in substantially the center of the casing.

I claim:

1. In a thermal cycling switch having a casing, a unitary assembly supported by said casing comprising:

a terminal secured to said casing;

a subassembly including a main bimetal and heater therefor carrying a cycling contact at one end thereof, said subassembly including means for pivotally securing its other end to said terminal;

an ambient compensating bimetal secured to said terminal and including a portion thereof extending in the general direction of said other end of said subassembly;

calibration and link means extending between said ambient compensating bimetal and a part of said subassembly free to move for adjusting the position of said cycling contact and also for serving as the link relating movement of said main bimetal and heater in accordance with movement of said compensating bimetal; and

said unitary assembly is supported from said casing solely through said securement of said terminal to said casing.

2. In a thermal cycling switch according to claim 1 wherein:

said extending portion of said ambient compensating bimetal is disposed in a generally face-to-face spaced apart relation to said subassembly.

3. In a thermal cycling switch according to claim 1 wherein:

said means for pivotally securing said subassembly includes a resilient leaf having one end secured to an end portion of said main bimetal and heater, and the other end secured to said terminal; and

said extending portion of said compensating bimetal extends only for approximately the length of said leaf so that heat transfer through a facing relationship of said heater and compensating bimetal is minimized.

4. In a thermal cycling switch according to claim 3 wherein:

said calibration and link means is adjustably carried by said extending portion of said compensating bimetal and bears against said subassembly at the junction between said leaf and the main bimetal and heater portion of said assembly. 

1. In a thermal cycling switch having a casing, a unitary assembly supported by said casing comprising: a terminal secured to said casing; a subassembly including a main bimetal and heater therefor carrying a cycling contact at one end thereof, said subassembly including means for pivotally securing its other end to said terminal; an ambient compensating bimetal secured to said terminal and including a portion thereof extending in the general direction of said other end of said subassembly; calibration and link means extending between said ambient compensating bimetal and a part of said subassembly free to move for adjusting the position of said cycling contact and also for serving as the link relating movement of said main bimetal and heater in accordance with movement of said compensating bimetal; and said unitary assembly is supported from said casing solely through said securement of said terminal to said casing.
 2. In a thermal cycling switch according to claim 1 wherein: said extending portion of said ambient compensating bimetal is disposed in a generally face-to-face spaced apart relation to said subassembly.
 3. In a thermal cycling switch according to claim 1 wherein: said means for pivotally securing said subassembly includes a resilient leaf having one end secured to an end portion of said main bimetal and heater, and the other end secured to said terminal; and said extending portion of said compensating bimetal extends only for approximately the length of said leaf so that heat transfer through a facing relationship of said heater and compensating bimetal is minimized.
 4. In a thermal cycling switch according to claim 3 wherein: said calibration and link means is adjustably carried by said extending portion of said compensating bimetal and bears against said subassembly at the junction between said leaf and the main bimetal and heater portion of said assembly. 